The present invention relates to a method of roll forming with using an in-line sweeping unit for bending roll formed structural beam components into non-linear non-planar shapes.
Roll forming apparatus exist that are capable of forming sheet into swept tubular structural beams. For example, Sturrus U.S. Pat. Nos. 5,092,512 and 5,454,504 and Lyons Published Application U.S. 2007/0180880 illustrate innovations where in-line sweep units at an end of a roll forming apparatus produce swept tubular bumper reinforcement beams. However, the apparatus of Sturrus '512 and '504 and Lyons '880 are limited to a single plane of sweep (also called “single plane of deformation”) and further are limited to sweeping in a single direction from a line level of the roll forming apparatus. Some structural products require sweeps in multiple directions and in different planes, rather than being limited to a single direction from line level or being limited to a single plane of deformation.
Notably, there are many difficulties in forming structural roll formed products in multiple directions. For example, sweeping in multiple directions requires multiple moving components, each adding complexity and tolerance issues as well as a nightmare of durability and maintenance problems. Further, when a structural product is bent in multiple directions, its “flat” wall sections tend to collapse and/or undulate in unpredictable directions, resulting in poor tolerance control and poor dimensional control. This is especially true where the roll formed material is high strength steel and/or where the beams have planar walls. Still further, where high strength steel is being formed, the loads and stress on machine components become very high, resulting in substantial maintenance and the need for constant repair. For example, structural beams and bumper reinforcement beams can be 80 ksi tensile strength steel (or higher), 2.2 mm thick (or thicker), and have a 3″×4″ (or more) cross-sectional envelop size. The forces resulting from attempts to sweep a beam of this makeup are extraordinarily high. The complexity increases still further if the sweep unit is expected to selectively sweep in multiple directions or planes, sweep at various selected times or longitudinal locations, and/or form relatively small radii, particularly where expected to do so “on the fly” at relatively high continuous line speeds of 100+ feet per minute. Notably, the automotive industry in particular has very tight requirements of dimensional consistency for bumper reinforcement beams and structural and frame sections, as well as high impact strength and high bending strength requirements.